FIG. 15 is a diagram showing an example of a conventional ion implantation apparatus disclosed in, for example Japanese Published Patent Application No. 62-241247. In FIG. 15, an ion beam 22 is applied to an ion implantation chamber 21 and corrected by an ion beam correcting lens 27. Thereafter, the corrected ion beam 22 passes through an ion beam measuring means 33 which functions as a sensor of a controller 32 for controlling the ion beam correcting lens 27. Then, the ion beam 22 passes through a Faraday cage 34 and is implanted in a disk 24 arranged on a rotary disc 23. This rotary disc 23 is connected to an ion beam ampere meter 26.
Then, operation thereof will be described in detail hereinafter.
The ion beam 22 is applied from the left side of FIG. 15 to the ion implantation chamber 21 and then implanted in the wafer 24 arranged on the rotary disc 23. The disc 23 serves as a bottom of the Faraday cage 34 and the amount of the ion beam applied to the Faraday cage 34 can be measured by the ion beam ampere meter 26 connected to the disc 23. The ion beam 22 passes through the ion beam correcting lens 27 and the ion beam measuring means 33 just before it reaches the Faraday cage 34.
FIG. 16 is a view showing the ion beam measuring means 33 seen from the side of the wafer 24. Referring to FIG. 16, a probe 29 formed of a high melting point metal is driven by a motor 40 so as to be rotated through an appropriate angle and vertically crosses the ion beam 22, whereby a current flows through the ampere meter 41. A potentiometer and a rotary encoder are attached to the motor 40 and then a signal obtained by the ampere meter 41 is monitored with an oscilloscope with appropriate synchronization, with the result that waveform shown in FIG. 17 is obtained. Thus, a vertical length, a position, and an approximate configuration of the ion beam can be obtained from the waveform and positions a and b in FIG. 17. The computer 32 receives this information and controls the ion beam correcting lens 27, whereby the ion beam 22 is corrected.
However, since the ion beam correcting lens 27 is inserted in front of the rotary disc 23 in the above conventional ion implantation apparatus, the size of the apparatus is increased and the structure thereof becomes complicated, with the result that production cost is increased. In addition, when the beam correcting lens 27 is inserted, the beam transporting distance is increased, so that the number of ions which collide with neutral particles and scatter is increased. As a result, transporting efficiency of the beam is reduced. In order to prevent it, the correcting lens has to be dispensed with so that the transporting distance of the beam may be short, particularly in a large current type ion implantation apparatus which relies on the transporting efficiency of the beam, like a predeposition type ion implantation apparatus (disclosed in, for example "Electron and Ion Beam Handbook") which is the main current present. However, if there is no ion beam correcting lens, it is difficult to appropriately control the current and current density of the ion beam.